The invention relates to a linear unit.
Such linear units move machine components, which are supported on the guide carriage, back and forth, for example. To this end, the threaded spindle is rotated by a motor or manually so that the spindle nut supported thereon, which is held in the guide tube, performs an axial movement that is oscillating, depending on the rotational direction of the threaded spindle. Of course, there is also the possibility to hold the guide carriage in the longitudinal groove of the guide tube in a rotationally fixed manner. In each case, the guide carriage and the spindle nut are securely connected with each other.
Up until now, extruded sections have been used as the guide tubes, which are typically made of a light metal. The guide slot is realized in the extruded sections by mechanical processing, preferably by milling. However, this type of processing is associated with significant labor, which includes both the milling and the subsequent refinishing such as burring or the like.
However, such processing can only be realized with significant expenditure, which, naturally, conflicts with a rational and cost-effective production required for guide tubes that are to be used as series parts in high quantities.
Therefore, DE 200 16 209 U1 proposes to realize the longitudinal slot in the guide tube at the time of extrusion so that, essentially, the mentioned work steps are not needed. As a consequence, an improvement over the above-mentioned state of the art is achieved.
However, relatively large tolerance must be put up with, which is unacceptable for certain applications.
In these cases, thick-walled precision steel tubes are used. However, these thick-walled precision steel tubes must be mechanically processed again, i.e., by cutting them to length via sawing, by facing their ends and by inserting the slot. In the latter case, a pre-milling step is performed at first. Then a milling step is completed and a burring step is performed. Finally, since steel tubes made of carbon steel are typically used, an electro-galvanizing process is required in order to keep the processed surfaces corrosion-resistant.
Overall, the known linear units are not suitable to meet all required conditions, both with respect to a cost-effective production and with respect to a high production accuracy.